Hi from Tennesee, USA.

I felt sorry for you when you said you hadn't grown watermelon! This is watermelon country. No garden is complete without a couple vines and people that grow nothing else grow watermelon. A general rule we use around here is if the cucumbers and pumkins will grow a watermelon will too. Their needs actually fall between and overlap the pumps and cukes.
There are literaly thousands of watermelon varieties. Some do well in hot, droughty conditions other thrive in cold and wet, and everything in between. There are varieties that only need 55 days from sprouting to over 100 days. Ignore the color of the flesh (every "Southerner" knows that watermelon taste is dependent on rain, sun, and soil, not color) and choose for your growing season. Obviously, you aren't going to grow 150 pound melon in less than two months, but the little ones taste better anyway and are easier to grow.
I realize it may be difficult to find the seed, I suggest you internet search for an heirloom seed provider in your country due to custom plant and seed restrictions.
Once you have your seed there are a few tiny rules. You can start them indoors in plantable pots like peat or newsprint pots, but not more than a week or two before they go outside. They will need to go out and harden for a week or so before planting. They should go into the garden two-three weeks after the last frost. You can also plant straight into the ground at this point and skip all the drama. Keep it watered well. A small piece of pipe at the base to use as a watering tube is a good idea if you are in a dry area. The leaves will droop to tell you if it needs more water. They are called 'water'melon for a reason.
This is the big rule never, never, never disturb the roots of a watermelon plant. It may not die if you are very gentle, but it will take longer to fruit and if it has already set fruit they often wither.
Also, I heard someone once (clearly not a resident of watermelon country) tell that you should pinch off extra blossoms to get a bigger fruit. Bigger yes, tastier no. In fact you will have almost no sugars and the texture is disgusting. Just let the vine decide how many fruit to set and you just keep it watered. Some manure tea would also be much appreciated, but it must not get on the vine or leaves. The absolute best fertilizer is rabbit manure raked into the soil just before planting.
The seed is very easy to save too!
